Lecture 2 - Variation

Question 1

What is a genotype?

Answer 1

the genetic makeup of an organism - underpins phenotype partly (also, the environment makes up phenotype)

Question 2

What is a phenotype?

Answer 2

Measurable characteristics of an organism from the genotype

Question 3

What does the nucleus consist of?

Answer 3

99% DNA 1% mitochondria

Question 4

What is DNA?

Answer 4

A molecule that has two strands - each mirrors the information in the other through base pairing.

Question 5

What bond is DNA held by?

Answer 5

Hydrogen bonds

Question 6

What is the backbone of DNA made up of?

Answer 6

sugar-phosphate backbone

Question 7

What is an allele?

Answer 7

An alternative version of a gene - - different alleles lead to formation of different form of protein

Question 8

How do we go from a gene to a protein?

Answer 8

1. Transcription - The DNA code is copied into a messenger RNA (mRNA) molecule.
2. Translation - The mRNA is read to build a protein from amino acids.

Question 9

How does the coding work?

Answer 9

4 bases of codes code for 20 amino acids

Question 10

A 3-base code gives how many amino acids?

Answer 10

1

Question 11

What is a codon?

Answer 11

Three code sequence that codes for an amino acid

Question 12

What is redundant coding

Answer 12

Multiple codons can code for the same amino acid.

Question 13

To what % of the genome in non-coding inter-gene regions?

Answer 13

60% - so 60% of what is in the genome is not genetic coding for a protein.

Question 14

What is an intron?

Answer 14

non-coding sequences inserted within the code for a particular protein

Question 15

What are exons?

Answer 15

coding sequences of cells that make up 1% of the full genome.

Question 16

Are most of the genome in humans coding or non-coding?

Answer 16

non-coding

Question 17

What is key about non-coding DNA?

Answer 17

Includes many transposable elements.
Includes many simple sequence repeats.

Question 18

How many base pairs are there in the human genome?

Answer 18

3.2 billion base pairs

Question 19

How many genes do humans have?

Answer 19

20,000-25,000 - around 27,000 base pairs long

Question 20

What is meiosis?

Answer 20

• Only one of each pair of chromosomes is copied and transferred
• creating 4 genetically varied gametes.

Question 21

What is mitosis?

Answer 21

part of the cell cycle where replicated chromosomes are separated into two new nuclei

Question 22

What is mutation and why does it occur?

Answer 22

It is a copying error due to meiosis and mitosis

Question 23

What are single-base substitutions?

Answer 23

DNA is made up of 4 bases: A, T, C, G. A single-base substitution means one of these is swapped for another.

Transition: same type -> same type (A purine is replaced with another purine)

Transversion: A purine is swapped with a pyrimidine, or vice versa.

Question 24

What are simple sequence repeat expansions?

Answer 24

a type of genetic mutation where short, repeating sequences of DNA are accidentally copied too many times during DNA replication.

Question 25

What are transposable element insertions?

Answer 25

copying of a transposable element such as Alu from one part of the genome to another

Question 26

What is segmental changes?

Answer 26

Extra chromosomes - down syndrome extra chromosome at 21

Question 27

Mutations that do have an effect are mainly..

Answer 27

deleterious/harmful - as it is a complex system

Question 28

What type of diseases to genetic mutations lead to?

Answer 28

Mendelian diseases

Question 29

What are 4 examples of mendelian diseases?

Answer 29

Cystic fibrosis Huntington's disease - has late onset systems Tay-Sachs disease - people with 2 copies get this disease, people with one copy are fine Haemophilia - mendelian diseases stay in the population and are passed down (usually not negative thing).

Question 30

How do you find the genetic basis of a phenotypic characteristic?

Answer 30

Linkage study: look at who is affected and who is unaffected within a large family, and trace which sections of which chromosomes are shared. Association study: Assemble large groups of individuals with and without the trait and compare the frequency of different alleles.

Question 31

What is a genome

Answer 31

the entire set of genetic material in an organism, including all its genes and non-coding DNA

Question 32

What are the three phases of genetics?

Answer 32

1. Classical genetics (Mendelian) 2. Molecular genetics (DNA structure/function) 3. Genomics (sequencing entire genomes)

Question 33

What are somatic cells and germ cells?

Answer 33

Somatic cells make more phenotype via mitosis. Germ cells (sperm and eggs) produce genotypes via meiosis.